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According to Wikipedia Centralized Traffic Control (CTC) is a signalling system used by railroads. The system consists of a centralized train dispatcher's office that controls railroad switches in the CTC territory and the signals that railroad engineers must obey in order to keep the traffic moving safely and smoothly across the railroad.

CTC systems are considered sufficient authority to run trains based strictly on signal indications. This is because CTC signals default to 'Stop' and require a human dispatcher to 'Clear' them.

ABS defaults to 'Clear' signals, and drops to 'Stop' if the block immediately beyond the signal is occupied, or if the switch (turnout) beyond the signal is set against the direction of traffic.

CTC is a layer superimposed over the basic ABS system to hold all signals in the 'Stop' aspect unless cleared by the dispatcher to their ABS value. This means that the local ABS logic will always (normally) supercede to the lower speed aspect. I.e. The dispatcher does NOT set the signals to green. He just permits them to go green.

ABS defaults to 'Clear' signals, and drops to 'Stop' if the block immediately beyond the signal is occupied, or if the switch (turnout) beyond the signal is set against the direction of traffic.

CTC is a layer superimposed over the basic ABS system to hold all signals in the 'Stop' aspect unless cleared by the dispatcher to their ABS value. This means that the local ABS logic will always (normally) supercede to the lower speed aspect. I.e. The dispatcher does NOT set the signals to green. He just permits them to go green.

'Clear' to the dispatcher means not stop. 'Normal' to the dispatcher is all signals at stop.

This clinic assumes that you understand the ABS signal system previously covered because that is the basis for the CTC operation.

We will NOT go step by step building the CTC panel. That in itself would require more time than we have. Instead we will start out with a completed example panel and first cover the operation of a CTC panel.

This clinic assumes that you understand the ABS signal system previously covered because that is the basis for the CTC operation.

We will NOT go step by step building the CTC panel. That in itself would require more time than we have. Instead we will start out with a completed example panel and first cover the operation of a CTC panel.

This clinic assumes that you understand the ABS signal system previously covered because that is the basis for the CTC operation.

We will NOT go step by step building the CTC panel. That in itself would require more time than we have. Instead we will start out with a completed example panel and first cover the operation of a CTC panel.

This clinic assumes that you understand the ABS signal system previously covered because that is the basis for the CTC operation.

We will NOT go step by step building the CTC panel. That in itself would require more time than we have. Instead we will start out with a completed example panel and first cover the operation of a CTC panel.

Clinic 2 will look at the underlying Logix that make it all work.

The CTCClinic1.xml panel has indicators for all the required logic.

The CTCClinic3.xml panel only includes prototypical indications, other than the traffic simulation toggles.

This panel includes many icons whos only purpose is to aid in understanding what is going on.

Traffic direction indicators. Some CTC panels do include traffic direction indicators for the single track sections. These lights are included as an aid to the dispatcher but are automaticly set and cleared.

This panel also includes traffic direction indicators in the passing areas to show the logic required for operation. This was not usually done for passing sidings, but was sometimes done for multi-track lines when traffic could normally be sent either way on the same line.

This panel also includes traffic direction indicators in the passing areas to show the logic required for operation. This was not usually done for passing sidings, but was sometimes done for multi-track lines when traffic could normally be sent either way on the same line.

CTC panels did not have actual signal indications. Operators could only infer aspects from the status of the panel lamps.

The Traffic Direction logic has also figured out that the main track has been reserved for righthand direction traffic. These lamps for the sidings are for clarification only, and do not normally appear on a prototype panel.

The Traffic Direction logic has also figured out that the main track has been reserved for righthand direction traffic. These lamps for the sidings are for clarification only, and do not normally appear on a prototype panel.

The train is getting closer, so the dispatcher clears the east end of his siding to let the train proceed into the next single track (also called intermediate) section without stopping.